Improve root set used by hat

[Kelly O'Hair]

I'll test this change:

diff --git a/src/share/classes/com/sun/tools/hat/internal/model/JavaStatic.java 
b/src/share/classes/com/sun/tools/hat/internal/model/JavaStatic.java
--- a/src/share/classes/com/sun/tools/hat/internal/model/JavaStatic.java
+++ b/src/share/classes/com/sun/tools/hat/internal/model/JavaStatic.java
@@ -57,7 +57,10 @@ public class JavaStatic {
              id = ((JavaObjectRef)value).getId();
          }
          value = value.dereference(snapshot, field);
-        if (value.isHeapAllocated()) {
+        if (value.isHeapAllocated() &&
+            clazz.getLoader() == snapshot.getNullThing()) {
+            // static fields are only roots if they are in classes
+            //    loaded by the root classloader.
              JavaHeapObject ho = (JavaHeapObject) value;
              String s = "Static reference from " + clazz.getName()
                         + "." + field.getName();


Let me know if that seems right.
Unfortunately,
we haven't many jhat tests, did you have any small testcase scenarios?

The few tests for jhat are at jdk/tests/sun/tools/jhat, I can help craft one
if you give me something to start with.

-kto

Keith Randall wrote:
> Here's a simpler patch that never makes Roots for these static fields in 
> the first place:
> 
> --- com/sun/tools/hat/internal/model/JavaStatic.java
> ***************
> *** 57,64 ****
>               id = ((JavaObjectRef)value).getId();
>           }
>           value = value.dereference(snapshot, field);
> !         if (value.isHeapAllocated() &&
> !             clazz.getLoader() == snapshot.getNullThing()) { // static 
> fields are only roots if they are in classes loaded by the root classloader.
>               JavaHeapObject ho = (JavaHeapObject) value;
>               String s = "Static reference from " + clazz.getName()
>                          + "." + field.getName();
> --- 57,63 ----
>               id = ((JavaObjectRef)value).getId();
>           }
>           value = value.dereference(snapshot, field);
> !         if (value.isHeapAllocated()) {
>               JavaHeapObject ho = (JavaHeapObject) value;
>               String s = "Static reference from " + clazz.getName()
>                          + "." + field.getName();
> 
> 
> On Wed, Oct 7, 2009 at 1:49 AM, Alan Bateman <Alan.Bateman at sun.com 
> <mailto:Alan.Bateman at sun.com>> wrote:
> 
>     A. Sundararajan wrote:
> 
>         I agree. Static fields of classes loaded by non-bootstrap
>         loaders should not be part of root set.
> 
>         PS. I am not sure  if this is a bug with hat or with heap
>         dumpers (the hotspot built-in dumper and SA's dumper). I don't
>         remember how "roots" is filled. May be, these static fields
>         should not be flagged as roots?
> 
>         -Sundar
> 
>     At least for the built-in heap dumper, static fields aren't
>     generated as roots (instead it's system classes and temporary
>     placeholders in the dictionary that are generated to the dump as
>     "sticky classes", to use a HPROF term). So I suspect this is more
>     likely to be a jhat issue.
> 
>     -Alan.
> 
>